240 
b. Eyein adult more than 1 mm. in longitudinal diameter. Lens over .5 mm. 
in diameter. Retina very simple, its maximum thickness 835 u in the old; the 
outer and inner nuclear layers consisting of a single series of cells each; the 
ganglionic layer of isolated cells. Maximum thickness of the outer nuclear layer 
Oe sOtthe AnNeril ayers. ye) Veckvee clin soe ato els ie aliere te atone teehee aerate cornutus 
bb. Eye in adult less than 1 mm. in longitudinal diameter. Lens less than 
.4mm. Outer nuclear layer composed of at least two layers of cells; the inner 
nuclear layer of at least three layers of cells, the former at least 10 » thick, the 
latter at least 18 ju. 
ce. Pigment epithelium 65 thick in the middle-aged, 102 in the old. 
papilliferus. 
cc. Pigment 49” thick in the middle-aged, 74-in the old; 24-30 per cent. 
thinner than in papilliferus: Bye!smaller ......¢00 22. .@s en soe agassizii. 
aa. The eye a vestige, not functional; vitreous body and lens mere vestiges ; 
the eye collapsed, the inner faces of the retina in contact; maximum diameter of 
eye about 200 y, 
d. No scleral cartilages; no pigment in the pigment epithelium, a minute 
vitreal cavity; hyaloid membrane with blood vessels. Pupil not closed. Outer 
nuclear, outer reticular, inner nuclear, inner reticular, ganglionic and pigment 
epithelial layers differentiated. Cones probably none. No eye muscles. Maxi- 
mum diameter of eye 180 ~. Eye probably connected with brain throughout 
DG oet vee: aM aact am tectces fete tohtety st MOH Sitintc ae setete oe sanettee lose EY Ney teccs aster “antes Typhlichthys. 
dd. Scleral cartilages; pigment in the pigment epithelium; vitreal cavity 
obliterated; no hyaloid membrane. Pupil closed. Some of the eye muscles 
developed. No outer reticular layer. Outer and inner nuclear layers merged 
into one. Eye in adult not connected with the brain. 
e. Pigment epithelium well developed; cones well developed; ganglionic 
cells forming a funnel-shaped mass through the center of the eye. Pigmental 
epithelium over the front of the eye without pigment. Maximum diameter of 
BY: ANIL DOO fe west ciricc 8 Lee vive SS co Stet ndg ss hale cist eee mete Ree Amblyopsis. 
ee. Pigment epithelium developed on distal face of the eye, rarely over the 
sides and back. Nocones. Nuclear layers mere vestiges; the ganglionic layer 
restricted to the anterior face of the eye just within the pigmented epithelium. 
Maximum diameter of the eye about 85 vw ...............0+22000e- Troglichthys. 
6. The structure of the vestigial eyes differs much in different individuals. 
7. The eye of Chologaster is an eye symmetrically reduced from a larger 
normal fish eye. 
8. The retina in Chologaster is the first structure that was simplified. 
